The present invention relates to the manufacture of tires. More particularly, it concerns a method and an apparatus for the manufacture of reinforcements for tires.
Tires are reinforced in particular by at least one ply known as a carcass ply, which today is most frequently disposed radially, anchored in each of the two beads having at least one bead ring each. The plies comprise a plurality of adjacent cords which, in the case of radial carcasses, are included approximately within a plane passing through the axis of rotation of the tire.
The expression "cord" is to be understood in its broadest sense, namely both as a single cord and a cable formed by the assembling of several single cords, or an equivalent assembly.
In the prior art, the most customary method consists in preparing, from a large number of spools of simultaneously unwound cords, plies the cords of which are oriented parallel to their greatest length and are embedded in rubber. These plies are then cut along a desired angle, for instance a right angle, into pieces of suitable length, whereupon the edges of the pieces of plies parallel to the cords are brought together, with or without superimposing of cords, in order to form intermediate or semi-finished products used upon the manufacture of the tire proper. The manufacture of such semi-finished products is illustrated, for instance, by U.S. Pat. No. 3,573,135. This method requires costly equipment and makes it necessary to manufacture a large number of different plies as a function of the widths of plies required by the sizes of tires to be produced.
In accordance with the state of the art, other manners of producing the reinforcements for tires are also known. According to one of such manners, the reinforcement cord or cords are disposed one after the other and continuously around a core which defines the inner surface of the tire, so as to form a tire reinforcement. Examples of this are to be found in U.S. Pat. Nos. 852,855, 1,328,006 and 1,321,402. However, the mechanization of the laying of the cord around a core is very complicated due to the fact that the cord develops in axial, radial and axial and radial directions in the space outside the core.
In accordance with another principle, the reinforcement cord is wound around two bead rings which are in their final circular shape or else are still slit and disposed flat while the cord is wound. This is illustrated, for instance, by Patents WO83/02749, U.S. Pat. No. 2,139,840 and U.S. Pat. No. 1,349,390. Here again, the method has numerous drawbacks related to the fact that a reinforcement is constructed which is very far from its final shape in the tire, particularly if it is constructed flat. In the event that the reinforcement is constructed around circular bead rings, it is necessary to effect a shaping by radial elevation of the central zone of the cords disposed between two bead rings, which is customarily done by means of pneumatic devices, and therefore lacks precision from the standpoint of respect for the geometry.
These known techniques for the manufacture of a reinforcement for tires from a single cord are therefore complicated and non-productive.